A one-pot method in water to synthesize a new cyanurate K(H 2 C 3 N 3 O 3 )·H 2 O with large birefringence

≈ 0.5 at 546 nm, which was confirmed by both DFT and experimental measurements. DFT reveals that the high birefringence arises from anisotropic polarizability associated with the π-conjugated isocyanurate layers, with minimal electronic contribution from the potassium cations. These findings highlight the isocyanurate group as a promising candidate for high-performance birefringence applications.